Devices for measuring a magnetic field are known.
Modern sensors for measuring magnetic fields are frequently in the form of fluxgate magnetometers. By way of example, there are two-axis or three-axis fluxgate magnetic field sensors which can measure magnetic fields in all spatial directions. In this case, there are three respective coils on two ferromagnetic cores. A triangular waveform generator generates a current which flows through the excitation coils. The current sets up a magnetic field in the ferromagnetic cores. The change in the magnetic flow induces voltages in what are known as the pickup coils. When no external field is applied, the difference between the voltages in the pickup coils is zero. As soon as an external magnetic field is set up, a difference voltage is produced.
This difference voltage is used in a magnetic field compensation system in order to actuate compensating coils. The magnetic field from the compensating coils, which are typically in the form of Helmholtz coils in apparatuses for compensating for magnetic fields, compensates for the external magnetic field.
Such fluxgate sensors are distinguished by high sensitivity and high resolution.
A drawback of apparatuses for compensating for magnetic fields with a fluxgate sensor is that the sensors normally have a very small bandwidth. Thus, the sensor bandwidth usually does not extend beyond 2 kHz.
Alternatively, the sensor used for measuring the magnetic field can also be a coil and the voltage induced in the coil by an external magnetic field can be measured. Such coil sensors are particularly suitable for relatively high frequencies, that is to say magnetic alternating fields, and are, by contrast, usually unsuitable for frequencies below 10 Hz. In addition, the signal from a coil sensor of this kind can be integrated into a digital signal processing system only very poorly. The high frequency of the measured alternating fields means that it would be necessary to provide a digital signal processing system having an extremely high sample frequency, which is complex and in many cases impossible.